In recent years, various attempts have been made to hinder, or ideally, substantially prevent formation of nitrosamines in tobacco products. Further, a number of attempts have been made to prevent exposing tobacco users to nitrosamines. For example, numerous filters have been employed in smoking tobacco products to at least generally attempt to filter out some of these nitrosamines. However, these efforts have not proved beneficial in smokeless tobacco products.
By way of introduction, fresh-cut, green tobacco has effectively no nitrosamines associated therewith. However, this fresh-cut, green tobacco is generally unsuitable for smoking and/or use in smokeless tobacco products such as chewing tobacco and/or snuff. In contrast, cured tobacco products manufactured in conventional manners are known to contain a number of tobacco-specific nitrosamines (TSNAs) such as N′-nitrosonornicotine (NNN), 4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanone (NNK), N′-nitrosoanatabine (NAT), and N′-nitrosonoanabasine (NAB).
The above-mentioned TSNAs are believed to be formed at least generally post-harvest, such as during and/or after conventional curing processes. More particularly, it is believed that an amount of TSNAs in a cured tobacco plant is at least generally dependent upon a presence of nitrites that accumulate on the plant during senescence (e.g., process of aging from full maturity to death of the tobacco plant's cells). Moreover, these TSNAs are believed to be formed during curing at least in part due to a chemical reduction of nitrates facilitated or at least generally catalyzed by exposure of the tobacco to an at least generally anaerobic (oxygen deficient) environment. This reduction of nitrates to nitrites is believed to occur via metabolic processes of micro flora, and more particularly, microbial nitrate reductase activity, associated with the tobacco plant under at least generally anaerobic conditions. The existence of such an at least generally anaerobic condition around the tobacco plant may be fostered by the fact that tobacco plants typically emit carbon dioxide during at least part of the curing process. Indeed, the reduction of nitrates to nitrites has been found to be particularly pronounced under humid conditions in which it is believed that the increased humidity increases a microbial load on the plant. In any event, once these nitrites are formed, the same are believed to combine with various tobacco-associated alkaloids, such as certain pyridine-containing compounds, in a process known as “nitrosation” to form nitrosamines such as those mentioned above.
One conventional method of curing tobacco, known as “flue curing,” at least generally involves placing tobacco plants, or at least the leaves thereof, in a curing barn and exposing the tobacco to convective heat in the form of one or more hot gaseous streams that includes combustion exhaust gases. When such convective heat is used to dry the tobacco, the combustion exhaust gases, such as carbon monoxide, carbon dioxide, oxides of nitrogen (e.g., NOx), and water are introduced to and may even be said to pass at least generally through the tobacco. It has been shown that exposure of the tobacco to such combustion gases during curing may produce tobacco specific nitrosamines through reactions of tobacco alkaloids with alternative nitrosating agents.
Another conventional curing method includes a variation of a flue curing process in which a heat exchanger is utilized. More particularly, fuel is burned to heat air, and the heated air is passed through flue pipes into a curing barn in which the tobacco plants are disposed. This generally results in a flow of heated air that passes through the curing barn. Moreover, this process utilizes primarily radiant heat emanating from the flue pipes to heat the air, thus substantially preventing exposure of the tobacco to combustion exhaust gases during curing.
Still another conventional curing method known as “air curing” generally involves placing the harvested tobacco plants in a curing barn and subjecting the plants to ambient air curing. This curing method is typically accomplished with little or no governance of environmental conditions. However, it is known to at least generally regulate airflow to at least roughly affect temperature and/or humidity in the curing barn.
Yet still another conventional curing method relates to a specific group of tobacco cultivars known as “dark fire tobaccos.” Typically, these dark fire tobaccos are harvested and hung in a curing barn while the leaves are yellow, green, or a combination thereof. A day or two after the tobacco is hung (and sometimes on the same day), the tobacco is exposed to heat and gaseous emissions (e.g., smoke) from combustion of appropriate materials such as wood and/or sawdust. This exposure is typically referred to as “dark firing” the tobacco and is generally done for several weeks. When the tobacco has reached a desired finish, the fire is extinguished, and the tobacco is allowed to come into order (or case) and subsequently removed from the barn for further processing. While the exposure of the tobacco to dark fire curing has traditionally been desirable to achieve a preferred flavoring of the tobacco, such conventional dark fire curing methods have not provided (or produced) tobacco products having reduced amounts of TSNAs.